Centrifuges used to separate components of different densities are known. During centrifugation, samples contained in tubes are spun at relatively high rates of speed. The resulting centrifugal forces on the samples cause denser material to move to the bottom of the tube. For example, in the case of a blood sample, the red blood cells move to the bottom of the tube, white blood cells form a layer over the red blood cells, and plasma forms a layer over the white blood cells. Other types of samples will form small pellets at the bottom of the tube.
Generally, centrifugation apparatus includes an electromechanical spinner having a bowl in which a rotor is disposed for rotation by a motor. The rotor includes a retention mechanism for restraining a plurality of tubes. One type of rotor is a "swinging bucket" type, in which the retention mechanism pivotably supports the tubes. With this arrangement, the tubes are loaded into the rotor in a substantially vertical position, but are free to swing outward in response to centrifugal forces so that resulting constituent layers or pellets are oriented substantially vertically in the tube. Another type of rotor is a fixed angle rotor, in which the retention mechanism supports the tubes at a fixed angle of inclination.
Under certain operating conditions, the load on the motor (i.e., the mass associated with the rotor, tubes, and fluid specimens) may be non-uniformly distributed around the circumference of the rotor. Such a non-uniform load distribution causes greater centrifugal forces at the circumferential location of the rotor with the greatest load mass.
Conventional rigid attachment of the motor to the spinner housing permits imbalanced centrifugal forces to be readily coupled to the housing in the form of vibration. Vibration in turn, disadvantageously results in accelerated motor wear and higher operating noise levels. Moreover, pivotal forces on the motor load resulting from imbalanced centrifugal forces tend to strain the motor shaft, thereby further accelerating motor wear. Other types of motorized apparatus in which motor load imbalances cause vibration suffer similar drawbacks from rigid motor attachment.